It's possible to set up a free of charge service/course and to do that you need to write 0 kr in the price option. You can follow these steps.

Step 1: To set up a service you need to click on service overview (on the left side of the screen) and then you click add service.

Step 2: When this window opens then you need to click on Add option 

3. Then you write 0 kr in the price option at the bottom of the page.